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Liu F.,University of Hawaii at Manoa | Huang G.,CAS Institute of Atmospheric Physics | Feng L.,National Marine Environmental Forecasting Center
Theoretical and Applied Climatology

In observations, the 2-day waves, identified as the convectively coupled equatorial inertio-gravity (IG) waves, only propagate westward. To understand this feature, a simple theoretical model is presented for the convectively coupled equatorial waves (CCEWs). Under the assumption that the convective heating is proportional to the vertical velocity on the first baroclinic mode, the nonlinear governing equation for the meridional velocity of the CCEWs can be derived. The optimal method is used to obtain the dispersion relation from this nonlinear equation, and the results show that the deep convection can slow down the IG waves by decreasing the mean state static stability, but the key leading to the westward propagation of the IG waves is the full meridional variation of the sea surface temperature (SST). The warm SST trapped near the equator excites long westward propagating IG waves, whereas the warm SST trapped near the ITCZ centered at 10° N excites short westward propagating IG waves. This theoretical model provides a simple tool to study the CCEWs in understanding the tropical circulation. © 2011 Springer-Verlag. Source

Li Y.K.,Beijing Normal University | Chao J.P.,National Marine Environmental Forecasting Center
Science China Earth Sciences

Assume that an oasis and its surrounding desert consist of an isolated system without mass and energy exchange with the outer environment. The characteristics of oasis evolution have been explored under the condition of system energy conservation. The results show that oasis evolves with two equilibrium states. The first equilibrium suggests a stable expansive and an unstable degraded oasis whereas the second equilibrium indicates a stable shrink and an unstable increase of the oasis area. If one equilibrium state is unstable, the components of the isolated system (oasis and desert) would tend to be no energy exchange and they each reach to energy balance respectively. Oasis would maintain its initial area in this case. Further analyses point out that the two equilibrium states have completely different characteristics. In the first equilibrium state, a higher vegetation albedo, lower soil albedo and larger canopy resistance, and direr soil both contribute to the oasis area expansion, accompanying an excessive large desert soil and vegetation canopy temperature difference (SCTD). In the second equilibrium state, however, a lower vegetation albedo, higher soil albedo and small canopy resistance, and wetter soil benefit the oasis area to stay near its initial value, following a moderate SCTD. The convergent trajectories of the initial values in phase space are influenced by the separatrices of the equilibrium points. Higher temperature is an advantage factor for initial values convergent to the oasis expansion solution. © 2014, Science China Press and Springer-Verlag Berlin Heidelberg. Source

Li Y.,CAS Research Center for Eco Environmental Sciences | Geng D.,CAS Research Center for Eco Environmental Sciences | Geng D.,China University of Geosciences | Liu F.,National Marine Environmental Forecasting Center | And 4 more authors.
Atmospheric Environment

Polyurethane foam (PUF)-disk based passive air samplers were deployed in King George Island, Antarctica, during the austral summer of 2009-2010, to investigate levels, distributions and potential sources of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in Antarctic air. The atmospheric levels of ∑ indicator PCBs and ∑ 14 PBDEs ranged from 1.66 to 6.50 pg m -3 and from 0.67 to 2.98 pg m -3, respectively. PCBs homologue profiles were dominated by di-PCBs, tri-PCBs and tetra-PCBs, whereas BDE-17 and BDE-28 were the predominant congeners of PBDEs, which could be explained by long-range atmospheric transport processes. However, the sampling sites close to the Antarctic research stations showed higher atmospheric concentrations of PCBs and PBDEs than the other sites, reflecting potential local sources from the Antarctic research stations. The non-Aroclor congener PCB-11 was found in all the air samples, with air concentrations of 3.60-31.4 pg m -3 (average 15.2 pg m -3). Comparison between the results derived from PUF-disk passive air sampling and high-volume air sampling validates the feasibility of using the passive air samplers in Antarctic air. To our knowledge, this study is the first employment of PUF-disk based passive air samplers in Antarctic atmosphere. © 2012 Elsevier Ltd. Source

Wan L.,National Marine Environmental Forecasting Center | Bertino L.,Mohn Sverdrup Center | Zhu J.,CAS Institute of Atmospheric Physics
Journal of Atmospheric and Oceanic Technology

The ensemble Kalman filter (EnKF) has proven its efficiency in strongly nonlinear dynamical systems but is demanding in its computing power requirements, which are typically about the same as those of the fourdimensional variational data assimilation (4DVAR) systems presently used in several weather forecasting centers. A simplified version of EnKF, the so-called ensemble optimal interpolation (EnOI), requires only a small fraction of the computing cost of the EnKF, but makes the crude assumption of no dynamical evolution of the errors. How do both these two methods compare in realistic settings of a Pacific Ocean forecasting system where the computational cost is a primary concern? In this paper the two methods are used to assimilate real altimetry data via a Hybrid Coordinate Ocean Model of the Pacific. The results are validated against the independent Argo temperature and salinity profiles and show that the EnKF has the advantage in terms of both temperature and salinity and in all parts of the domain, although not with a very striking difference. © 2010 American Meteorological Society. Source

Liu F.,CAS Institute of Atmospheric Physics | Liu F.,University of Hawaii at Manoa | Huang G.,CAS Institute of Atmospheric Physics | Feng L.,National Marine Environmental Forecasting Center
Theoretical and Applied Climatology

To understand the nature and role of multi-scale interaction involved in the Madden-Julian oscillation (MJO), a dynamical model is built based on two essential processes: the convective complex of the MJO modulates the strength and location of synoptic-scale motions, which in turn feed back to the MJO through the convective momentum transfer (CMT). Our results exhibit that: (1) The lower tropospheric easterly CMT coming from the 2-day waves slows down the MJO dramatically; (2) although the lower tropospheric westerly CMT coming from the superclusters can produce the horizontal quadrupole vortex and vertical westerly wind-burst structures of the MJO, it drives the large-scale motions to propagate eastward too fast; (3) the planetary boundary layer provides an instability source for the MJO and pulls the MJO to propagate eastward at a speed of 0~10 ms -1; and (4) the optimal structure of the multi-scale MJO should be: the stronger superclusters/2-day waves prevail in the rear/front part of the MJO and produce lower tropospheric westerly/easterly CMT there. These theoretical results emphasize the role of CMT and encourage further observations in the multi-scale MJO. © 2011 Springer-Verlag. Source

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